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Hitler planned a submarine to outperform all others. The Type 21 was the world's most advanced submarine: Hitler's sea-faring super weapon.
Hitler planned a submarine to outperform all others. The Type 21 was the world's most advanced submarine: Hitler's sea-faring super weapon.
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00:00In the battle for supremacy at sea, the Nazis wage a war of technology.
00:14It was one of the most influential designs of a German weapon technology in the Second
00:20World War.
00:21Hitler orders the development of secret weapons beneath the waves.
00:25With this we will greatly undermine the enemy's naval tactics.
00:30Fast, silent and deadly.
00:33There's a potential for hitting 18 ships inside 20 minutes.
00:40The Nazis build giant structures to protect these terrifying machines.
00:44It goes on for about a quarter of a mile that way.
00:47The scale is just breathtaking.
00:51They'll revolutionize naval warfare forever.
00:54The Type 21 U-Boat was the one weapon that could have been a real game changer.
01:01This is the story of Hitler's killer subs.
01:08The biggest construction projects of World War II, ordered by Hitler to secure world
01:14domination.
01:17Now they survive as dark reminders of the FĂŒhrer's fanatical military ambition.
01:23These are the secrets of the Nazi megastructures.
01:40Cruiserhead is an escort of destroyers.
01:44Periscope depth will go under the escort.
01:50Escort ace, Captain Adalbert Schnee, is on patrol in Germany's deadly new Type 21 U-Boat.
01:57I can see them, they're only 600 meters away, and they have no idea that we are here.
02:13Today the only surviving example of Hitler's underwater superweapon lies docked in a port
02:19in northern Germany.
02:21This is the Type 21 U-Boat, and she is completely unlike any submarine that's come before.
02:29She's shaped like a blade rather than a boat.
02:31She's sleek, she's streamlined, she was designed to fight underwater.
02:37She's a terrifying new weapon of war.
02:41Nick Bradby, a specialist in submarine architecture, is examining the weapon that changed the face
02:46of submarine warfare.
02:52This was the reason for the Type 21 going to sea.
02:56It's got 20 torpedoes in this room ready to go.
02:58It'll be absolutely devastating.
03:03The story of Hitler's super submarine begins in 1935.
03:10After the First World War, the Versailles Treaty bans Germany from building submarines.
03:17Hitler tears up the treaty.
03:19He's determined to expand his armed forces, including building new U-Boats.
03:30When war breaks out in 1939, Hitler has 57 submarines, a small but deadly fleet.
03:39In the five months from June to October 1940 alone, Nazi U-Boats sink 311 Allied ships.
03:53Buoyed by this success, U-Boat Chief Rear Admiral Karl Dönitz demands more.
04:04To destroy British morale, we have to reduce their control of the sea and thereby cut their
04:11lines of communication.
04:16The very life of the British nation depends on them.
04:20U-Boats are absolutely key to Germany's chance of strangling Britain's overseas merchant
04:28trade, which is so key to ultimately winning the war.
04:32And Dönitz, Admiral Dönitz, is constantly lobbying the Kriegsmarine general staff and
04:38saying, please, let me build us some more U-Boats.
04:41U-Boats is the key.
04:42And he's absolutely right.
04:45Hitler needs no persuading.
04:47He orders the immediate expansion of the U-Boat building program.
04:53Over the next three years, the Nazis will build a force of over 350 U-Boats.
05:00They will cover the entire Atlantic Ocean, from America to the Mediterranean and from
05:06the Arctic to the South African coast.
05:12The mainstay of the U-Boat force is the Type 7.
05:18It's small, cheap and quick to build.
05:23One model stands out as the main attack vessel.
05:32Standing on a remote beach on Germany's Baltic coast is the last remaining example of this
05:37fearsome piece of Nazi technology.
05:43This is the Type 7C.
05:50And it's all about this bow.
05:54This is designed more like a ship.
05:56It's designed to run on the surface for nearly all of its life.
05:59This prow shape makes it faster and makes it ride more easily in the waves.
06:05It was also designed to fight on the surface.
06:09It was armed with guns.
06:12There was an 88mm deck gun up forward for firing on other ships.
06:20And an anti-aircraft armament up on the fin.
06:27So here we have the boat's propeller shafts.
06:29There's two of these, one on each side.
06:31And they drive these propellers.
06:34Now, they may not look very big, but there's enough power going through them to drive the
06:37boat up to 17 knots.
06:40The Type 7C's speed on the surface is up to 8 knots faster than many Allied ships.
06:47It can easily outmanoeuvre the merchant convoys.
06:51But what makes the Type 7C so deadly lies deep within its bow.
07:01Aha!
07:04Right, well, this is the forward torpedo room.
07:07And this is one of the torpedoes, the G7E.
07:12There were eight of these things stored in this room.
07:15And they weigh a tonne and a half.
07:17It's a huge weight to shift around.
07:19And to reload it, to get it lined up to go into one of these tubes, you'd have ten,
07:24twelve people just having to haul this thing up, just by hand and by mechanical advantage.
07:32The Type 7C carries 14 torpedoes.
07:41Once the captain's decided what he's going to shoot the torpedo at, he's got to pass
07:45the instructions for how deep he wants it to run, how fast he wants it to run, and what angle.
07:51A sailor can use this device to programme the torpedo's guidance system from here.
07:57And then again, when the captain wants to take the shot, that can't be done centrally from the control room.
08:02It's a manual release.
08:04Someone has to come stand here, safety off, and then fire.
08:21And finally, right here at the back end of the boat, she's got a sting in the tail.
08:26This is a fifth torpedo tube, pointing backwards.
08:29So once she's discharged her forward four in an attack on a convoy, if she has an escort chasing her down,
08:34or if she's fired her first four and then turned away to make a fifth attack,
08:38she can fire a fifth torpedo from this tube.
08:45U-boat captains like Adalbert Schnee attack mostly at night.
08:49When a surfaced U-boat is barely visible.
09:12If they're spotted, they can quickly disappear back beneath the waves.
09:19Dive!
09:26Early in the war, the Type 7s have incredible successes.
09:30But Admiral Dönitz has even greater plans.
09:34To utilise advanced technology and destroy the Allies at sea.
09:41In early 1941, the secret Nazi weapons programme is developing a new U-boat.
09:47One with the potential to inflict serious losses on Allied shipping.
09:55It's the brainchild of Dr Helmut Walter, a pioneering German engineer.
10:01Helmut Walter is a genius, there's no question about that whatsoever.
10:05Helmut Walter is a genius, there's no question about that whatsoever.
10:08And the Germans are very good at recognising that and rewarding that.
10:12Walter has been developing rocket propulsion units for use in both submarines and aircraft since 1934.
10:22His most famous construction is the rocket motor that powers the Messerschmitt Me 163 aircraft.
10:30The engine is powered by Walter's secret weapon.
10:34A super fuel he's created using the volatile chemical hydrogen peroxide.
10:40In a U-boat, this fuel has the capability to drive it faster and allow it to stay submerged for longer.
10:48A submarine that uses diesel engines has to be on the surface in order to run those engines.
10:53A peroxide powered submarine can run its engines at full power at whatever depth it likes.
10:58Dönitz secures funds for Walter to develop a practical vessel to test his submarine ideas.
11:05The experimental craft is codenamed the V-80.
11:11Walter designs a hull the shape of a figure 8.
11:16The lower section is used to store the hydrogen peroxide fuel.
11:21The upper section houses the engines and crew.
11:28To improve the V-80's performance underwater, Walter also designs a streamlined outer hull with no external weapons to reduce drag.
11:39It had a new shape for submarines, a shape which was described at the time as more fish-like than ship-like.
11:46In initial trials, the vessel reaches underwater speeds of 23 knots, three times faster than the Type 7.
11:58By November 1941, Walter is ready to demonstrate the V-80 to his paymasters in naval high command.
12:11Measuring just over 72 feet in length, this small boat now reaches the incredible speed of 28 knots submerged.
12:22Dönitz recognises the potential.
12:25He recommends naval high command fully support Walter in his groundbreaking work.
12:32The V-80 was a huge breakthrough in propulsion technology, but it was far too small to be a combat U-boat.
12:38It didn't have the range, it couldn't carry the weapons.
12:41Walter starts modifying the design.
12:45He will take the best of the V-80 and turn it into a weapon of war.
12:56Meanwhile, Dönitz has a plan to make his existing fleet even more deadly.
13:07For the first year of the war, U-boats hunt alone.
13:12But in 1940, after the fall of France, the Nazis established naval bases on the country's west coast...
13:20...and used high-tech radio communications to implement a devastating strategy.
13:27The subs will attack allied convoys in large groups, known as wolf packs.
13:35The point of the wolf pack is to get as many U-boats as you possibly can together, working in coordination with one another...
13:41...for maximum effect on that convoy of, say, approximately 40 merchant vessels.
13:47You're going to hit more and destroy more if there's, say, seven U-boats working together than if there's just one.
13:55Dönitz knows tightly controlled wolf packs will generate maximum destruction.
14:03For these to work effectively, he needs a dedicated communications center to coordinate attacks.
14:10In 1940, the Nazis take over a chateau in the French countryside.
14:16It's the perfect base from which to direct U-boat tactics.
14:23Historian James Holland is exploring the secrets of Rear Admiral Dönitz's U-boat nerve center.
14:30It's a really rather lovely chateau, but it sort of reminds me a little bit of those First World War days...
14:36It sort of reminds me a little bit of those First World War generals in their chateau HQs.
14:42On the other hand, I suppose he was the head of the German navy, so you wouldn't really expect him to slum it.
14:49Chateau de Pignerol is strategically located between Paris and all of the main coastal U-boat bases.
14:58Its control hub lies in a network of structures that the Nazis added.
15:07This is going underneath the garden of the chateau.
15:13It's some 400 feet long, about 120 yards or something like that.
15:18I've been told there's three foot of concrete above this and then a further three foot of soil,
15:24so the roof of this is about six foot under the garden.
15:29The tunnel leads up a stairway to a separate bunker complex on the surface.
15:35This nerve center relayed orders between naval high command in Berlin and the U-boats.
15:42What I'm looking for is the main big room, the main communications room.
15:47What's down here?
15:53I think I found it. I think this must be it.
15:56This is where the signals come from the U-boats to here and back out again to sea.
16:02It's amazing to think that back in the war this would have just been a hive of activity.
16:07You'd have had lots of desks along the walls and people with telexes and Enigma machines.
16:16The complex comprises 11 bomb-proof bunkers.
16:19Built to protect over 1,000 communications staff who maintain constant contact with Dönitz's U-boat fleet.
16:27It feels solid. You'd feel safe down here.
16:32I keep saying down here, but of course you're not. You're actually above ground.
16:36It feels like you're in the depths of the earth, but in actual fact this is above ground level.
16:41Under Dönitz's command, in the first two years of the war, U-boat successes steadily increase.
16:48Germany is on the brink of starving Britain into submission.
16:58In 1941, Nazi U-boats sink 501 ships.
17:04U-boat aces like Captain Schnee are the sharp shooters of the sea.
17:09The convoy is holding course. Distance one kilometer.
17:12Good. All in position?
17:14In position.
17:16Using stealth tactics to stun the enemy, even the order to fire is issued in the wake of the war.
17:24The U-boats have been used for decades.
17:27Using stealth tactics to stun the enemy, even the order to fire is issued with a whisper.
17:36Target set. Tube 1 ready.
17:38Tube 1 ready.
17:40Tube 1 go.
17:44Tube 2 fire.
17:46Tube 2 go.
17:52Target hit. It's sinking.
17:57The U-boats have the upper hand.
18:04But then Allied military and technological advances redress the balance of power in the Atlantic.
18:12The Allies managed to miniaturize radar equipment enough to mount it in aircraft.
18:17And this is terrible for the U-boats.
18:19Airborne radar allows aircraft to spot U-boats far outside the range at which the aircraft itself can be seen.
18:26And then the U-boat is attacked without warning.
18:35And having occupied Iceland, the Allies have another key advantage.
18:41Unfortunately for the U-boat crews, that's a strategic base that the Allies can use with airfields,
18:48which suddenly means that the northern part of the Atlantic, that's covered by aircraft.
18:52And aircraft can then sweep over that stretch of the Atlantic, looking and spotting for U-boats.
18:59Now the Allies can get a fix on U-boat positions.
19:03The hunters become the hunted.
19:11And in spring 1942, Captain Schnee discovers just how vulnerable his U-boat is
19:17when it surfaces off the east coast of the United States.
19:23Where the hell did that come from?
19:25Close the hatch, prepare to dive!
19:27Close the hatch.
19:29Dive!
19:34They know how to find us.
19:37They know where we are.
19:39Schnee's U-boat escapes.
19:42But to Hitler's concern, Nazi losses increase.
19:46Tell me, what's the state of the submarine war?
19:52Because of Allied air cover, we are being pushed out into the Atlantic Ocean.
19:57That severely reduces our strike rate.
20:00What about our losses?
20:03In the Bay of Biscay, we are incurring ever-growing losses through air attacks.
20:08We need to outrun them, and not be seen.
20:12And not be seen.
20:16In 1943, the German Navy loses a record 244 U-boats.
20:23And over 10,000 men.
20:27The U-boat force is failing.
20:31But Dönitz and Hitler are determined to win back the initiative
20:35with a plan that will revolutionize submarine warfare forever.
20:43U-boat ace Adalbert Schnee is one of the men Dönitz tasks with leading his new strategy.
20:54Reassigned to U-boat headquarters in Paris,
20:57Schnee is responsible for organizing operations against Allied convoys.
21:03But to regain the upper hand, he needs new technology.
21:07Can you bring me file 93, please?
21:12Excellent, thank you.
21:16The Type 7 is now outdated and outgunned.
21:21It's not very streamlined.
21:23You can see all of these features here.
21:25The big saddle tanks for the diesel fuel,
21:27the handrails around the bridge, the anti-aircraft guns,
21:31even the vents to drain the casing of flood water.
21:33All of these just added to drag when it was underwater.
21:37The water running past them slowed the boat down,
21:40and that meant the Type 7 couldn't be very fast underwater.
21:43But worse, as well as slowing the boat down,
21:46these features all created noise.
21:48Water flowing over them created turbulence,
21:50and that increased the boat's signature,
21:52made it easier to hear on sonar.
21:55Added to this, the Type 7's two diesel engines need air to run,
22:00so they're only used when there's no wind.
22:03They're used when the ship is on the surface.
22:08When submerged, the Type 7 must use an alternative power source,
22:13and its speed is much slower.
22:17When she's submerged, through here,
22:19we've got the electrical control panels,
22:21and these two electric motors,
22:23one on each side, one for each shaft.
22:25Now, these draw power from the batteries
22:27and drive the boat when she's underwater.
22:29They can't go nearly as fast, only five or six, maybe seven knots.
22:31And there's not that much power in the batteries.
22:35When they run down, the boat is forced to the surface
22:38to power up the diesel engines that recharge the batteries.
22:42If they keep their speed down to four knots,
22:44they can stay down for maybe a day.
22:46If they really eke it down to two knots, barely walking pace,
22:49they could eke it out to two, maybe three days.
22:51But that's the limit of their endurance.
22:55But Admiral Dönitz has a solution.
22:58The rocket-powered submarine technology of engineering genius,
23:03Helmut Wolter.
23:10To regain the initiative against the Allies,
23:13Admiral Dönitz is planning a new breed of submarine.
23:21We have a solution.
23:23There is a successful draft for a new submarine
23:27with greatly increased underwater speeds.
23:31This will make the enemy U-boat chasers entirely ineffectual.
23:36If that was the case, it could be revolutionary.
23:40May I suggest we develop this new type of submarine as quickly as possible?
23:45I'm backing you completely.
23:48With this, we will greatly undermine the enemy's naval tactics.
23:57Wolter has the green light to build a larger combat boat,
24:01based on his old V-80.
24:03He calls it the Type 18.
24:07But once construction begins, issues arise.
24:13One of the greatest problems is with the vessel's high-tech hydrogen peroxide fuel.
24:18A fleet of Type 18s would have required a huge amount of hydrogen peroxide to fuel them,
24:23an amount which Germany just could not produce.
24:27With no guaranteed fuel supply, plus a problem with turbine construction,
24:31the project is shelved.
24:36Despite this setback, Wolter's main concept will not die.
24:41The principles behind it, this idea that you could create a submarine
24:45that is truly a submarine and not a submersible,
24:47that can actually operate faster under the water than it can on the surface,
24:52that is what is truly revolutionary.
24:57U-boat engineers Friedrich Schurer and Klaus Broeking
25:01take Wolter's Type 18 design a step further
25:05with the Type 21.
25:12The idea is to maintain Wolter's revolutionary streamlined
25:16figure-eight hull design for the new craft.
25:20Electric and diesel engines drive the Saab,
25:24but with an added twist.
25:27In the hull's lower section sit massive batteries,
25:31three times the size of those in the Type 7.
25:35The Type 21 will measure over 251 feet in length
25:40and 21 feet in width.
25:43It's more than twice the size of the Type 7.
25:51Hitler gives the new vessel priority over all other submarine construction.
25:58Naval High Command set a target for 15 submarines to be completed each month.
26:05But Dönitz demands more.
26:08He's determined to build the Saab more quickly.
26:14In July 1943, he agrees to the appointment of a specialist engineer
26:19to manage the construction.
26:21I am aware that he hasn't worked on something like this before,
26:25but I don't think that matters.
26:27He understands mass production. That's the key here.
26:32His name is Otto Merker.
26:35He's had great success in mass-producing cars and fire trucks
26:41and believes he can build the Type 21 in the same way.
26:51His idea is to make it in three stages.
26:57First, the main shell of the U-boat is built in nine separate sections.
27:03But to protect these hull sections from Allied air attack,
27:07Merker spreads their manufacture across 32 factories throughout Germany.
27:14These are located close to waterways
27:17to provide transportation for the huge sections.
27:21Once completed,
27:23Merker sends the sections to 11 different fitting outyards
27:27for stage two of the build,
27:29the installation of gearing, electric motors
27:33and specialized submarine equipment.
27:38Merker then sends the completed parts to one of three yards,
27:42located in Danzig, Hamburg and Bremen,
27:46where the nine sections are welded together.
27:51Despite this ingenious plan,
27:55Merker calculates the process will take up to nine months.
28:01For the Nazis, it could be too late.
28:12To speed up Type 21 production,
28:15Merker orders an additional construction facility,
28:18one capable of housing an entire production line.
28:22Built to withstand Allied bombs,
28:25it'll be the ultimate U-boat factory.
28:30Commissioned in 1943,
28:33Valentin bunker sits by the river Weser, near Bremen.
28:37It's the largest bunker built by the Nazis in Germany.
28:41This whole structure, it goes on for about a quarter of a mile that way.
28:45The scale is just breathtaking.
28:50Its walls are 23 feet thick,
28:54and the roof is up to 15 feet thick.
28:59James Holland has come to explore inside this concrete monster.
29:04I can honestly say I've never seen anything quite so large.
29:09The scale of this place is truly, truly enormous.
29:16One can only imagine how something of this size
29:20could possibly be built in just 22 months.
29:26Merker divides this massive structure into 13 separate bays.
29:31Each one will carry out one part of the assembly process.
29:34Bays 12 and 13 are watertight,
29:37and can be flooded for underwater tests.
29:41Once complete, Type 21s will launch into the river Weser.
29:50And this is the finished product.
29:54A Nazi mega-weapon unlike anything that has gone before.
29:59The Type 21.
30:01Up here on the upper deck, it's really obvious how clean everything is.
30:06The streamlining is really apparent.
30:09We can see the clean lines down the side.
30:12And these bollards are really the only significant obstructions on the upper deck.
30:17When the boat went to sea, these would be dropped down under the casing,
30:21so the deck would be flush and smooth.
30:24And similarly with these handrails.
30:27They're really important while we're walking around on the upper deck,
30:29but these could be dismounted and taken down below.
30:36We're coming up to the front now, the bow of the deck.
30:39It's not a boat-shaped bow like previous submarines had.
30:42It just comes to this sort of rounded forward end.
30:46And we've got here, these are the forward hydroplanes.
30:49These are used to control the boat's depth.
30:51And at high speed, they can be folded away, flush into these slots here.
30:56Although she's much bigger than the Type 7,
30:59amazingly, the streamlined hull produces a smaller acoustic signature,
31:04making it harder for enemy sonar to detect her.
31:08But it's the technology housed within this futuristic casing
31:12that makes the Type 21 revolutionary.
31:17So this is the powerhouse of the submarine.
31:20This is an absolutely massive electric motor.
31:225,000 horsepower drives the propellers,
31:26enough to achieve 17 knots submerged.
31:30The Type 7 can only do 6 or 7 knots underwater,
31:33so this is two and a half times as fast.
31:35It's a huge step forward.
31:37And that's really what allows the Type 21 to fight underwater.
31:42Aha!
31:44So these are batteries.
31:47This is really what makes the Type 21 the Type 21.
31:52236 tonnes of batteries fill the lower hull,
31:56enough to power the boat for 11 days.
32:01This is a pretty big space.
32:04And it's a pretty big space.
32:07This is a pretty big space.
32:10And this is only one side of it.
32:13There's a whole other side through there.
32:17And then there's another level down below.
32:21These are basically just giant car batteries.
32:24Unfortunately means they store loads of energy.
32:27They need loads of regular maintenance while they're in use.
32:30Now, there's a narrow passageway here between the two battery tanks.
32:35And some poor sailor would have to come down this passageway,
32:39climb up through one of these holes and lie on this board.
32:44And then he'd be able to scoot himself backwards and forwards
32:48because this thing runs on rails.
32:51But while he was doing that in this cramped space,
32:54he had to be really careful not to touch these exposed live electrical connectors.
33:00There's more than enough energy in this battery to kill you.
33:05The Type 21's two diesel engines can recharge the batteries within just five hours.
33:12They require air to run, so are only used on the surface
33:17or at periscope depth, thanks to the snorkel.
33:22This new invention allows air to enter the sub when just below the surface.
33:29But the Type 21 snorkel is ingenious.
33:33It has a ball valve to stop water entering the boat
33:37and it provides an indirect air feed to the engine.
33:42The clever thing that Volta did with this design was
33:46the inlet pipes don't directly connect to the diesel.
33:49Air can come in down these pipes and it comes out here,
33:53directly above the engine's air filter.
33:55The pipes feed air into the boat itself
33:58and the diesel draws air from the atmosphere of the boat.
34:00That means if a wave goes across the top of the snorkel mast
34:04and the valve closes, then the diesel can keep running for a little while
34:08by just using up the air in the boat.
34:10It means that unlike the Type 7,
34:12the Type 21 engines can remain running underwater even in the roughest sea.
34:19But the 21's innovative construction and groundbreaking technology
34:24have only one real purpose.
34:27It's all about her firepower.
34:31This is the business end of the Type 21.
34:34This is its main weapon system.
34:36We've got six 21-inch torpedo tubes.
34:39There's a pair up here, a pair down here,
34:41and another pair below the floor.
34:43Now, each of these can be loaded with a torpedo.
34:48This is a really hefty weapon.
34:50It's got about a quarter of a tonne of explosive in the front end.
34:53That's a huge warhead.
34:55These are really one-shot, ship-killing weapons.
34:58And the Type 21 carries 20 of them.
35:01Six pre-loaded in the tubes,
35:03and another 14 in the torpedo room behind it.
35:07So while the Type 21 had more torpedo tubes than the Type 7,
35:11the real advance was its automatic reloading system.
35:15It could reload all six of its torpedo tubes in less time
35:18than the Type 7 could have reloaded a single tube.
35:20This submarine could have fired 18 torpedoes into a convoy in 18 minutes.
35:24It had the potential to be absolutely devastating.
35:28The Type 21 is quieter and deeper diving than any submarine that has come before.
35:35And it's faster submerged than most merchant convoys travelling on the surface.
35:41The submarine is a lethal weapon.
35:46One that Hitler's been waiting for.
35:48But the Allies step up their bombing campaign targeting Nazi heavy industry.
35:53It means steel is in short supply.
35:58There was also the army crying for guns, for small arms, for tanks,
36:04for all kinds of equipment.
36:07The Air Force crying for airplanes and the like.
36:11It was trying to have a very small cake,
36:14and trying to feed an abundance of hungry mouths from it.
36:24Allied aircraft prowl the coastline,
36:27making any testing of the new submarine impossible.
36:31They bomb Hamburg heavily, destroying three Type 21s in the harbour.
36:37And then turn their attention to the Nazis' biggest enemy,
36:41and then turn their attention to the Nazis' biggest U-boat construction facility.
36:55In March 1945, Allied aircraft drop their bombs on Valentinbank.
37:05Evidence of these attacks litters the assembly bays.
37:09Goodness, look at that. That's absolutely amazing.
37:14That must have been where one of the two Grand Slams
37:18that hit the roof and penetrated through, struck.
37:22And look at all the debris around. Oh my goodness, what's this?
37:27This must be the last remains of the Grand Slam.
37:32This is a ten-tonne bomb.
37:35This is the biggest thing the RAF can carry.
37:38Designed by Barnes-Wallace, who of course designed the bouncing bomb.
37:43And look at the thickness of it.
37:47That's heavy. That's just a fraction of it. I can barely lift that up.
37:52This is called an earthquake bomb.
37:55The idea is that the weight of it, the force of it, hits the roof,
37:59penetrates through a huge amount,
38:02and then there's a delayed fuse, and then it explodes.
38:05So it goes through about ten of the fifteen feet of the thickness of that roof.
38:11Then it explodes, and that's what does it. That's what causes this.
38:15And with the two bombs, there's a thousand tonnes of concrete that comes down.
38:21And really, for the Valentin assembly plant, that's it.
38:30Dönitz's ultimate U-boat factory is finished.
38:33Before it even begins production.
38:36It's a devastating setback.
38:42The three remaining assembly yards are now under increased pressure
38:46to get Type 21s off the production line.
38:52Between June 1944 and April 1945,
38:56119 Type 21s are delivered in full working order.
39:04But due to lengthy crew training, only two go into active service.
39:13Dönitz places one under the command of U-boat ace Adalbert Schnee.
39:21After two months getting to know his new vessel,
39:24he's now in charge of the most advanced submarine in the world.
39:29On the 30th of April 1945,
39:32Schnee guides his craft silently out of a Norwegian fjord,
39:36heading for the Atlantic Ocean.
39:43He's back on patrol, seeking out enemy shipping.
39:50But back in Germany, the war has finally caught up
39:54with Dönitz and his submarine fleet.
39:56The Red Army has sacked Berlin.
39:59And Hitler is dead.
40:02On the 4th of May 1945,
40:05Dönitz makes a radio broadcast to his U-boats.
40:10U-boatsmenner, men of the U-boat force,
40:14after a heroic fight which knows no comparison in history,
40:19you have put down your weapons.
40:22You have achieved things which others have never achieved.
40:26You can't hurt them.
40:28The greatest sacrifice for your fatherland you are yet to make.
40:32No shadow will be cast on your honour,
40:35but your fatherland will be spared the worst consequences.
40:40But Schnee has one last chance to demonstrate
40:43the capabilities of this technological marvel.
40:49Heading back to Norway, he picks up the sound of a propeller.
40:54It's from the HMS Norfolk.
41:05Cruiserhead is an escort of destroyers.
41:09We'll go under the escort.
41:14Periscope depth. Yes. Good.
41:18Schnee lines up the Norfolk in the crosshairs of the Periscope.
41:24I can see them. They are only 600 metres away.
41:30Submerged and silent, the U-2511 is almost invisible.
41:37And they have no idea that we are here.
41:41It's a tempting moment.
41:48But the ceasefire has been called.
41:53Schnee chooses not to disobey orders.
41:57That's it.
42:00The war is over.
42:03Bring the boards up.
42:06We're going back home.
42:09In Germany, Dönitz gives orders to scuttle any completed Type 21s
42:15to prevent them falling into enemy hands.
42:1984 are destroyed.
42:22But it's not enough.
42:25The Allies get their hands on the Type 21.
42:29It becomes the model for the world's first nuclear-powered sub,
42:33the USS Nautilus.
42:35In this regard, it was certainly one of the most successful
42:39and influential designs of German weapon technology
42:43in the Second World War.
42:46In a bitter irony, the Nazis had created
42:50the most advanced underwater superweapon in history.
42:54But it arrived too late to save Germany
42:58and never even fired a single torpedo at the enemy.
43:02If the Type 21 had entered the Battle of the Atlantic
43:06two years earlier, in 1943,
43:09it's difficult to imagine how the Allies could have maintained
43:12convoys across the Atlantic.
43:15There was no technology that could find, could destroy it.
43:18But the Type 21 entered the war just too late to make a difference.
43:27Post-war, Admiral Dönitz served a 10-year service
43:30After his release, he wrote his memoirs
43:34and then sank into relative obscurity.
43:38Captain Schnee served six months in a minesweeper unit
43:42before reinventing himself as a salesman.
43:46An ignominious end for two giants
43:49of the Nazis' U-boat Battle of the Atlantic.
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